When energy prices fluctuate, small scale storage, such as provided by electric vehicles or uninterruptible power supplies, allows users to reduce their overall costs by buying in price troughs. However, if future prices are rising, a user may be inclined to store energy long-term. By analysing the structural properties of the charging schedule for energy storage systems, this paper demonstrates that long-term storage is optimal only if prices are rising extremely rapidly. The tools and methods described in this report is part of a broader investigation into the application of data networking concepts in energy networks.